1. Field of the Invention
The invention relates to a liquid crystal display device, and more particularly, to a liquid crystal display device having an improved aperture ratio and a method of fabricating the same.
2. Discussion of the Related Art
Generally, a liquid crystal display (LCD) device uses optical anisotropy and polarization properties of liquid crystal molecules. The liquid crystal molecules have a definite alignment direction as a result of their thin and long shapes. The alignment direction of the liquid crystal molecules can be controlled by applying an electric field across the liquid crystal molecules.
In other words, as the intensity or direction of the electric field is changed, the alignment of the liquid crystal molecules also changes. Since incident light is refracted based on the orientation of the liquid crystal molecules due to the optical anisotropy of the liquid crystal molecules, images can be displayed by controlling the light transmittance of the liquid crystal material.
Since the LCD device including thin film transistors as a switching element, referred to as an active matrix LCD (AM-LCD) device, has excellent characteristics of high resolution and displaying moving images, the AM-LCD device has been widely used.
The AM-LCD device includes an array substrate, a color filter substrate and a liquid crystal layer interposed therebetween. The array substrate may include a pixel electrode and thin film transistor, and the color filter substrate may include a color filter layer and a common electrode. The AM-LCD device is driven by an electric field between the pixel electrode and the common electrode to have excellent properties of transmittance and aperture ratio. However, since the AM-LCD device uses a vertical electric field that is perpendicular to the substrates, the AM-LCD device has poor viewing angles.
An LCD device having a wide viewing angle property has been suggested and developed to resolve the above-mentioned limitations.
FIG. 1 is a cross-sectional view of a related art LCD device. As shown in FIG. 1, the related art LCD device includes an upper substrate 9 and a lower substrate 10 spaced apart from and facing each other. A liquid crystal layer 11 is interposed between the upper and lower substrates 9 and 10. A common electrode 17 and a pixel electrode 30 are formed on the lower substrate 10. The common electrode 17 and the pixel electrode 30 may be disposed on the same level. Liquid crystal molecules of the liquid crystal layer 11 are driven by a horizontal electric field L, which is induced between the common and pixel electrodes 17 and 30. Although not shown in the figure, a color filter layer is formed on the upper substrate 9. The upper substrate 9 including the color filter layer may be referred to as a color filter layer. The lower substrate 10 including the common electrode 17 and the pixel electrode 30 may be referred to as an array substrate.
FIGS. 2A and 2B are cross-sectional views showing turned on/off conditions, respectively, of a related art LCD device. As shown in FIG. 2A, when the voltage is applied to the LCD device, arrangement of liquid crystal molecules 11a above the common electrode 17 and the pixel electrode 30 is unchanged. However, liquid crystal molecules 11b between the common electrode 17 and the pixel electrode 30 are horizontally arranged due to the horizontal electric field L. Since the liquid crystal molecules 11b are arranged by the horizontal electric field L, the LCD device has a wide viewing angle property. For example, the LCD device has a viewing angle of about 80 degrees to about 85 degrees up and down and right and left without an image inversion or a color inversion.
FIG. 2B shows a condition when the voltage is not applied to the LCD device. Because an electric field is not induced between the common and pixel electrodes 17 and 30, the arrangement of liquid crystal molecules 11 of the liquid crystal layer is not changed.
FIG. 3 is a plan view schematically illustrating a pixel region of a related art LCD device, and FIG. 4 is a cross-sectional view taken along the line IV-IV of FIG. 3.
As shown in FIGS. 3 and 4, an array substrate of the related art LCD device 40 includes a gate line 43, a common line 47 and a data line 60 on a first substrate 41. The gate line 43 is formed along a horizontal direction, and the common line 47 is parallel to the gate line 43. The data line 60 crosses the gate line 43 and the data line 47 and defines a pixel region P with the gate line 43.
A thin film transistor Tr is formed at a crossing portion of the gate and data lines 43 and 60. The thin film transistor Tr includes a gate electrode 45, a semiconductor layer 50, a source electrode 53 and a drain electrode 55. The source electrode 53 extends from the data line 60, and the gate electrode 45 extends from the gate line 43.
Pixel electrodes 70 and common electrodes 49a and 49b are formed in the pixel region P. The pixel electrodes 70 are electrically connected to the drain electrode 55 through a drain contact hole 67. The common electrodes 49a and 49b are parallel to the pixel electrodes 70 and are alternately arranged with the pixel electrodes 70. The common electrodes 49a and 49b extend from the common line 47.
A color filer layer 85 is formed on an inner surface of a second substrate 81 of a color filter substrate opposite to the array substrate. An overcoat layer 87 is formed on the color filter layer 85. A black matrix 83 is formed to correspond to boundaries of each pixel region P.
Here, the common electrodes 49a disposed adjacently to the data line 60 may be referred to as outer common electrodes. In this case, the outer common electrodes 49a are spaced apart from the data line 60 with a pre-determined distance, more particularly, more than 3 μm. This is to minimize effects on an electric field induced between the common electrodes 49a and 49b and the pixel electrodes 70 due to the data line 60. Further, this is to prevent a parasitic capacitance between the outer common electrodes 49a and the data line 60.
Therefore, light leakage may occur in an area between the data line 60 and the outer common electrodes 49a, and to prevent the light leakage, the black matrix 83 of the color filter substrate has a width such that the black matrix 83 overlaps the data line 60 and the outer common electrodes 49a. However, the aperture ratio of the pixel region p is lowered due to this structure.